1. Field of the Invention
The present invention relates to a unit for sterilizing strip material on a packaging machine for packaging pourable food products, and to a packaging machine comprising such a unit.
2. Brief Description of the Related Art
Machines for packaging pourable food products, such as fruit juice, wine, tomato sauce, pasteurized or long-storage (UHT) milk, etc., are known in which packages are formed from a continuous tube of packaging material defined by a longitudinally sealed strip.
The packaging material has a multilayer structure comprising a layer of paper material covered on both sides with layers of heat-seal material, e.g. polyethylene. In the case of aseptic packages for long-storage products such as UHT milk, the packaging material comprises a layer of barrier material defined, for example, by an aluminium film, which is superimposed on a layer of heat-seal plastic material and is in turn covered with another layer of heat-seal plastic material which eventually defines the inner face of the package contacting the food product.
For producing aseptic packages, the strip of packaging material is unwound off a reel and fed through sterilizing unit in which it is sterilized, for example, by immersion in a bath of liquid sterilizing agent such as a concentrated solution of hydrogen peroxide and water.
More specifically, the sterilizing unit comprises a bath filled, in use, with the sterilizing agent in which the strip is fed continuously. The bath conveniently comprises two parallel vertical branches connected at the bottom to define a U-shaped path of a length depending on the traveling speed of the strip and such as to allow enough time to treat the packaging material. For effective, fairly fast treatment, so as to reduce the size of the sterilizing chamber, the sterilizing agent must be maintained at a high temperature of, say, roughly 70xc2x0 C.
The sterilizing unit also comprises an aseptic chamber in which the strip of packaging material issuing from the sterilizing bath is subjected to mechanical processing (e.g. by drying rollers) and thermal/fluidic processing (e.g. by hot-air jets) to remove any residual sterilizing agent. The amount of residual sterilizing agent allowed in the packaged product, in fact, is governed by strict standards (the maximum permissible amount being in the order of a few parts per million); and the aseptic chamber must be maintained slightly above ambient pressure to ensure any leakage through the seals occurs outwards as opposed to inwards of the chamber to keep out any contaminating agents.
Before leaving the aseptic chamber, the strip is folded into a cylinder and sealed longitudinally to form in known manner a continuous, vertical, longitudinally sealed tube. The tube of packaging material, in fact, forms an extension of the aseptic chamber and is filled continuously with the pourable product and then fed to a forming and (transverse) sealing unit for forming individual packages and by which the tube is gripped between pairs of jaws to seal the tube transversely and form aseptic pillow packs.
The pillow packs are separated by cutting the sealed portions between the packs, and are then fed to a final folding station where they are folded mechanically into the finished form.
Packaging machines of the above type are used widely and satisfactorily in a wide range of food industries; and performance of the sterilizing unit, in particular, is such as to amply conform with standards governing asepticity of the packages and residual sterilizing agent.
Within the industry, however, demand for further improvement exists, especially as regards elimination of residual sterilizing agent, and which stems, in particular, from market demand for packages featuring reclosable opening devices which are easy to open and provide for easy pouring of the product.
In the case of nonaseptic packaging machines, such devices are applied, e.g. injection molded directly, to the strip material before the packages are formed.
Conversely, in the case of aseptic packaging machines, any opening devices are normally applied after the packages are formed, which poses drawbacks from the production standpoint by requiring the use of sophisticated systems for supplying and applying the opening devices. That is, if applied beforehand to the strip, the opening devices form breaks in the geometric continuity of the strip, in which residual sterilizing agent may become trapped, and from which the sterilizing agent cannot be removed completely using known techniques.
On the other hand, the use of additional means for removing the sterilizing agent may have a negative effect on the operating parameters of the aseptic chamber, in particular temperature and pressure, thus impairing performance of the sterilizing unit.
It is an object of the present invention to provide a unit for sterilizing strip material, in particular on a machine for packaging pourable food products, designed to provide an effective, straightforward, low-cost solution to the above problems.
According to the present invention, there is provided a unit for sterilizing strip packaging material on a packaging machine for packaging pourable food products, the unit comprising a bath for containing a sterilizing agent in which the packaging material is fed continuously; an aseptic chamber having an input connected to an output of said bath; and a main air-processing circuit comprising first suction means for aspirating air from said aseptic chamber, air processing and purifying means, and blowing means for blowing the processed air into said aseptic chamber; characterized by comprising an auxiliary recirculating circuit comprising second suction means for aspirating air from said aseptic chamber, and nozzle means connected to said second suction means and located close to an input of said aseptic chamber to direct a jet of air onto at least one predetermined portion of said packaging material.
Withdrawing aseptic air from the aseptic chamber and feeding it back into the chamber provides for effectively removing additional residual sterilizing agent with as little effect as possible on the operating parameters of the chamber, and so enabling the formation of aseptic packages with opening devices applied beforehand to the strip material, while at the same time eliminating any residual sterilizing agent. Moreover, using the aseptic air already in the sterilizing unit on the machine, the system is extremely straightforward and inexpensive by not requiring dedicated aseptic-air producing and processing systems.
The present invention also relates to a packaging machine for producing aseptic packages of pourable food products from strip packaging material, the machine comprising a sterilizing unit having a main air-processing circuit comprising first suction means for aspirating air from said aseptic chamber, air processing and purifying means, and blowing means for blowing the processed air into said aseptic chamber, and an auxiliary recirculating circuit in turn comprising second suction means for aspirating air from said aseptic chamber, and nozzle means connected to said second suction means and located close to an input of said aseptic chamber to direct a jet of air onto at least one predetermined portion of said packaging material.
According to a preferred embodiment of the present invention, the machine preferably comprises a unit for applying opening devices upstream from said sterilizing unit.